Males exploited for sex: mother nature's revenge

An Australian orchid has been exposed as a master of sexual deception, luring male wasps by emitting the same heady scent that female wasps use to seduce potential partners.

The hapless males get nothing in return as they fly from orchid to orchid attempting to mate with the plants, but in reality just pollinating them.

Rod Peakall, of the Australian National University, said the native species, Chiloglottis trapeziformis, relied exclusively on this devious strategy for pollination.

"It's an unfair system. They exploit the wasps," he said.

Dr Peakall and his colleagues unmasked the chemical trickery by comparing extracts from the orchids and from the heads of the females of the wasp that exclusively pollinates them, Neozeleboria cryptoides.

They identified a single compound that was produced by both. This was the first example of a plant having evolved an exact copy of an insect sex pheromone, Dr Peakall said. "It is a new class of chemical not previously known to science."

To confirm its seductive power, the team, which includes researchers in Germany, coated black plastic beads with a synthetic version of the compound. Males wasps were attracted to these beads but not to odourless ones. The study was published yesterday in the journal Science.

Orchids in Australia and Europe are the only plants known to use sexual deceit to ensure pollination, with some species also having flowers that resemble the shape and hairiness of insects they want to attract.

Dr Peakall, who was awarded a $390,000 five-year Australian Research Council grant this week to study the evolution of sexual deception in orchids, said most plants provided food such as nectar to insects in return for pollination. But about 30 per cent of orchids rorted the system.

The Chiloglottis trapeziformis orchid was interesting to scientists from an evolutionary point of view, because production of its unique wasp-seducing chemical was likely to depend on only a single gene and a mutation could make it attractive to a different insect, Dr Peakall said. "So the process of evolution of a new species could be very simple."